When people refer to Microsoft as "PC" even though PC refers to a "personal computer" and has nothing to do with operating system.
When people write tan^-1 instead of acrtan.
When my physics teacher uses 9.80 as acceleration due to gravity instead of 9.81.
When my physics teacher pronounces kinetic with a long i.
When my physics teacher rounds to less than three decimal places.
When people say they're never going to use algebra even though I use it all the time.
When people say math is stupid just because they don't understand it.